Predicting Cereal Disease Risks for 2023
Diseases in all crop types have been commonly observed in 2022, particularly in wheat. The manifestation of these diseases has been due largely to the consecutive wet seasons allowing the build-up of fungal inoculum, coupled with high humidity during key crop stages facilitating infection. The following diseases were the most commonly seen and which will require specific management practices to reduce the chance of yield loss during 2023. The use of a Predicta B test can be used to help identify any diseases which may be present but not visible.
Stripe Rust
Widespread Stripe Rust infections in 2022 have stemmed from the ideal conditions for infection, the trafficability issues preventing timely fungicide applications, plus newly detected pathotypes that are highly virulent on certain recently released varieties including Rockstar, Vixen, Catapult, Bennett and Boree.
Infections cause a loss of green leaf area and subsequent reduction in photosynthetic potential. Under the right conditions, an infection event during flowering can cause floret sterility and/or pinched grain.
Spores can travel vast distances by wind and rain splash can spread the disease throughout the crop canopy.
Reduced sensitivity to fungicide had been detected in rust, so it is expected that resistance may develop in future.
Growing resistant varieties is the best management practice to reduce infection and the reliance on fungicides.
For highly susceptible varieties or where high infection pressure is expected, the use of an in-furrow fungicide, followed by foliar fungicides at growth stage Z31 and Z39 may be required.
Crown Rot
Crown Rot causes yield loss in cereals due to restricting moisture flow from the roots to the head during grain fill. It is often observed as individual white heads, with a brown or pink discolouration of the crown. Moist autumn conditions coupled with a dry spring favour disease expression.
Cereal crops ranging from least sensitive to most sensitive are barley > bread wheat > triticale > durum. Wheat varieties also display a variation in susceptibility to the disease. Therefore, under high disease pressure situations and where wheat is required to be grown, a more resistant variety should be chosen.
Inoculum levels are directly correlated with stubble loads during the early post-emergent phase of the crop. Reducing the chance of stubble contacting seedlings is the most effective method of reducing disease occurrence. Burning stubble and inter-row sowing are ways of achieving this.
Most winter growing grasses host Crown Rot.
Most fungicides are not effective in controlling Crown Rot, however they can provide some disease suppression.
Cultivation will damage the Crown Rot hyphae and reduce infection. Disc seeders can be particularly problematic as they generally operate in high stubble load environments and do not cultivate the soil.
Early sowing should reduce the yield loss associated from Crown Rot infection.
A single year of broadleaf crop is not reliable in reducing the inoculum levels significantly. However, a “double break” of two successive broadleaf crops does appear to be effective in managing the disease.
Fusarium Head Blight
Fusarium Head Blight is caused by the same fungus as the Crown Rot fungus.
Head Blight occurs when spores from the crown travel up the plant and infect the flowering head, leading to sterile heads or pinched grain which can look white or pink. Receival standards have very low thresholds for infected grain, reflecting minimal human consumption or feed markets available for the grain due to Mycotoxin risk.
Infected seed can also cause Seedling Blight which can reduce seedling germination and vigour. Do not use infected grain as seed.
Inoculum levels are directly correlated with Crown Rot risk, therefore practices that reduce Crown Rot susceptibility should reduce the instances of Head Blight.
Most fungicides are not effective in controlling Head Blight, though a very well timed “Head Wash” fungicide may provide some suppression.
Currently there is little genetic resistance in varieties suitable to grow in Southern NSW.
Septoria Tritici
Septoria is a fungal disease which infects leaves, causing lesions that reduce green leaf area.
Significant yield losses can occur in susceptible varieties under the right environmental conditions.
Spread of the disease occurs through spores being released from stubble and blown onto crops, plus rain splash from infections lower in the canopy
Infection risk is greatest under cool, wet conditions and prolonged humidity of the crop canopy 48hrs > 95% humidity.
Reducing the intensity of cereals in the rotation and growing varieties with resistance are the best methods of preventing the disease. Foliar fungicides can also be effective in preventing the spread of the disease.
Take-all
Take-all is a cereal disease most often observed post flowering, by the premature haying off of patches within the crop. Affected plants generally contain no grain, are easily pulled from the ground and have a blackened crown. Yield loss in severe cases can be in excess of 50%.
Wheat and triticale are most susceptible, with barley and oats less affected.
Paddocks most at risk are those which were in a cereal in 2022 or those which were previously a grassy pasture. Growers with seeders providing limited cultivation and those having soil pH levels above 5.0, are at an even greater risk of infection.
Moisture over summer will reduce inoculum levels for next season.
Grass weeds over summer can build up Take-all levels if soil temperatures are cool.
One clean break crop will significantly reduce inoculum levels in seasons with adequate moisture.
Later sowing will lead to greater breakdown of inoculum.
Reducing pre-emergent herbicides can reduce severity of Take-all, as the crop has a more resilient root system.
Fungicide treatments on the seed and fertiliser can reduce infection levels.
Adequate nutrition may help reduce the severity of the disease.
Rotation of broadleaf crops with cereals is the most effective long term control measure.
Rhizoctonia
Rhizoctonia is a soil born fungal disease which causes root pruning, being most prominent in dry seasons due to the reduced access to nutrients and moisture. The greatest yield losses are normally seen in good seasons.
Barley is the most severely affected, followed by wheat, triticale and oats.
Grassy pastures and intensive cereal rotations increase levels of inoculum.
Wet spring and summer conditions will help breakdown inoculum prior to sowing, provided that weeds are controlled during the fallow.
Sowing as early as possible with a tyned seeder can help minimise Rhizoctonia infection.
Fungicide applied to the seed or fertiliser can also reduce infection rates.
Avoidance of pre-emergent herbicides which cause root pruning will also help to reduce disease severity.
Longer term control is achieved through sound crop rotations.
Management Strategies
Management for each specific disease may require different strategies. The key factors to consider include:
Selecting varieties with the greatest genetic resistance /tolerance.
Sound crop rotations, limiting cereal on cereals and incorporating a double broadleaf crop break where possible.
Removing stubble via burning removes significant proportion of leaf borne disease inoculum. Cultivation can also have the same affect.
Cultivation with tyned seeders rather than disc seeders can disrupt soil borne fungal hyphae
Sowing timing to maximise the early vigour of the crop to compete with disease challenges.
Fungicides applied to either seed or fertiliser, plus foliar applied fungicides to limit yield penalties from disease infection.